Automatic calibration system for computer-aided surgical instruments

ABSTRACT

A system for automatic calibration of instruments (S) having varying cross-sectional dimensions within a predetermined range and having detectable elements ( 110, 112, 113, 114 ) thereon for computer-aided surgery, comprising a calibration base (C) having detectable elements ( 43, 44, 46, 48 ) secured thereto for detecting a position and an orientation thereof in space by sensors ( 204 ) connected to a position calculator ( 202 ). The calibration base is adapted to receive and to releasably secure a working shaft ( 100 ) of any of the instruments (S) and provides an abutting surface ( 14 ) for a tip ( 102 ) thereof in such a way that a position and orientation of the tip ( 102 ) of the instrument (S) secured therein is calculable when working shaft cross-section dimensions thereof are known. The position calculator ( 202 ) receives instrument data ( 214 ) and calibration data ( 218 ) from an operator through a user interface ( 206 ) and stores the instrument data ( 214 ) and calibration data ( 218 ) for subsequent calibrations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to computer-aided surgery instrumentationand, more particularly, to the calibration thereof.

2. Description of the Prior Art

In computer-aided surgery, it is known to use surgical instrumentsdetectable by positioning systems in order to have an on-screenrepresentation of the instrument with respect to an operated part of apatient's body. It is readily understood that great amounts of precisionand accuracy are required in the space positioning of the surgicalinstruments in order to obtain reliable representation of the operation.A misrepresentation of the instrument with respect to the patient's bodymay have dramatic consequences and may even be fatal to the patient.Thus, prior to computer-aided surgery, the instruments must becalibrated.

One known method of calibrating is referred to as the axial-conicalcalibration. This method consists in achieving pre-determined maneuverswith a surgical instrument having detectable devices thereon for it tobe located in space by sensors connected to a position calculator.Namely, a first maneuver consists in rotating the surgical instrumentwith respect to its longitudinal axis, whereby the position of thelatter is set. During this rotation, the position calculator receivesreadings which will allow it to calculate a transform matrix from thepositioning system to the axis of the instrument. Thereafter, in asecond maneuver, the instrument is rotated according to a conicaltrajectory having as an apex the working tip thereof. Hence, thepositioning system may interpret and find another transform matrixbetween the positioning system and the tip of the surgical instrument.Although the axial-conical calibration method is simple, the requiredmaneuvers of calibration may take a few minutes to an inexperienced userand the position calculator may require to repeat the maneuvers if theyare judged as being unsatisfactory.

Calibration systems having permanently calibrated instruments have beenprovided in order to avoid lengthy steps of calibration. In suchsystems, a working field is scanned by sensors connected to a positioncalculator which recognizes the geometry of a given surgical instrument,whereby it is calibrated.

Precautions must be taken when using permanently calibrated instrumentsto ensure that these are not altered or damaged, whether it be inpre-surgery sterilization or during surgery. The instruments are subjectto frequent manipulations during surgery, and thus, having sensors ordetectable devices thereon involves the possibility that the position ofthese sensors or detectable devices is altered, whereby precision islost in the space representation of the instrument. In this case, aninventory of equivalent instruments must be on hand during surgery incase of damage or alteration to an instrument. It would thus bedesirable to have a calibration system allowing frequent calibrating byits simplicity and its rapidity of execution, to better suit thesurgical room environment.

SUMMARY OF THE INVENTION

It is an aim of the present invention to provide a method forautomatically calibrating surgical instruments which is simple and rapidin use and which produces a calibration of constant precision tofacilitate the calibrating.

It is a further aim of the present invention to provide a method forautomatically calibrating surgical instruments which includes validatingthe calibration.

It is a still further aim of the present invention to provide anapparatus for automatically calibrating surgical instruments whichaccommodates a wide range of instruments.

It is a still further aim of the present invention to provide anapparatus for automatically calibrating surgical instruments and capableof sustaining sterilization.

Therefore in accordance with the present invention, there is provided acalibration base to automatically calibrate instruments having varyingcross-sectional dimensions within a predetermined range forcomputer-aided surgery. Each of the instruments has detectable means, aworking shaft and a tip at an end of the working shaft. The calibrationbase comprises detectable means secured thereto for detecting a positionand an orientation thereof in space by sensors connected to a positioncalculator. The calibration base is adapted to receive and to releasablysecure the working shaft of any of the instruments. The calibration baseprovides a first abutting surface for the tip thereof in such a way thata position and orientation of the tip of any of the instruments securedtherein is calculable when working shaft cross-section dimensionsthereof are known, whereby any of the instruments is calibrated when theposition of the tip of the working shaft thereof is calculated.

Also in accordance with the present invention, there is provided amethod for calibrating the above described calibration base. The methodcomprises the steps of (i) detecting a position and orientation in spaceof the detectable means of the calibration base and of the instrument bythe sensors, (ii) receiving instrument data including eitheridentification data relating to instrument cross-sectional dimensiondata stored by the position calculator or of instrument cross-sectionaldimension data to be stored by the position calculator for subsequentcalibrations, and (iii) calculating a position of a tip of any one ofthe instruments secured in the calibration base with respect to thedetectable means of the calibration base whereby the instrument iscalibrated with respect to the detectable means of the instrument.

Further in accordance with the present invention, there is provided asystem for automatic calibration of instruments for computer-aidedsurgery. The system comprises a calibration base as described above.Sensors detect a position and orientation in space of the detectablemeans of the calibration base and of the instrument. The positioncalculator as described above is connected to the sensors forcalculating a position and orientation of the tip of the working shaftof the instruments secured in the calibration base with respect to thedetectable means thereon whereby any of the instruments is calibratedwith respect to the detectable means on the instrument when the positionof the tip of the working shaft thereof is calculated.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the nature of the invention, referencewill now be made to the accompanying drawings, showing by way ofillustration a preferred embodiment thereof, and in which:

FIG. 1 is a perspective view of an automatic calibration unit with atool in accordance with the present invention;

FIG. 2 is a top plan view, partially cross-sectioned, of the automaticcalibration unit with an optically detectable tool;

FIG. 3 is a fragmented side elevational view of an example of aninstrument tip disposed on the automatic calibration unit;

FIG. 4 is a fragmented side elevational view of another example of aninstrument tip on the automatic calibration unit;

FIG. 5 is a fragmented side elevational view of a further example of aninstrument tip on the automatic calibration unit;

FIG. 6 is a block diagram illustrating a method of automaticallycalibrating surgical instruments in accordance with the presentinvention; and

FIG. 7 is a perspective view of the automatic calibration unit with atool in accordance with a further embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a calibration base C supporting asurgical instrument S. The calibration base C comprises a base plate 10having a bottom flat surface 12. The base plate 10 also defines an XYplane 14. For clarity purposes, XYZ axes have been added to the drawingsin order to clearly identify the space orientation of planar elements.For instance, the XY plane 14 is planar with respect to the XY axesprovided therewith. Also, it is noted that the calibration base Cgenerally consists in a material which must be able to sustain severalcycles of autoclave sterilization, such as a stainless steel. Someelements of the calibration base C will require to be made of othermaterials and will be identified herein as such.

A vertical wall 16 extends perpendicularly from the XY plane 14 of thebase plate 10. A first panel 18 projects from a top portion of thevertical wall 16 and shares a top edge surface 20 therewith. A firstprotrusion 22 and a second protrusion 24 protrude from a proximalsurface 26 of the vertical wall 16 and of the first panel 18, and areadjacent the top edge surface 20 thereof.

As best seen in FIG. 2, the first panel 18 defines an XZ plane 28 on theback of the proximal surface 26. The XZ plane 28 is perpendicular withrespect to the XY plane 14. Referring now to both FIGS. 1 and 2, asecond panel 30 is shown extending perpendicularly from the XZ plane 28of the first panel 18, and thereby defines a YZ plane 32. The YZ planeis perpendicular with the XZ plane 28, and thus with the XY plane 14.The XZ plane 28 and YZ plane 32 intersect at an edge line 34.

As best seen in FIG. 2, a top bulge 36 and a bottom bulge (not shown)extend horizontally (i.e. in the XY plane) from the top and bottom ofthe second panel 30, with a lever 38 pivotally disposed therebetween.The lever 38 has rounded ends 40 and 42 at its extremities. A spring(e.g. torsion spring) is shared between the lever 38 and the secondpanel 30 such that the lever 38 is biased toward the edge line 34 at theintersection of the XZ plane 28 and the YZ plane 32. The lever consistsin a material able to sustain the high-pressure of an autoclave duringthe sterilizing of the calibration base C, such as an acetal copolymer.

Returning to FIG. 1, detectable spheres 44, 46 and 48 are secured to theproximal surface 26 of the vertical wall 16 and the first panel 18. Thedetectable spheres are coated with a retro-reflective layer in order tobe detected by, for instance, an infrared sensor using axialillumination. It is pointed out that other shapes are known and couldalso be used as alternative embodiments to retro-reflective spheres. Asan example, straight cylinders, corner reflectors or the like havingretro-reflective properties could also be used. It is also noted thatthe detectable spheres 44, 46 and 48 may be removed by providingsnap-fit mating adapters such that single-use spheres may be used. Thisallows for the spheres to be sterilized with processes milder thanautoclave sterilization, whereby a coating does not need to becharacterized by its capability to sustain high temperatures orpressures.

Still referring to FIG. 1, the surgical instrument S is shown having ashaft 100 of circular cross-section. A tip 102 is disposed at a workingend thereof, whereas a handle 104 is disposed at a handling end thereof.Referring to FIGS. 3, 4 and 5, tips of various tools in accordance withthe present invention are shown at 102. Returning to FIG. 1, an arm 106extends from the handle 104 of the surgical instrument S. A blade 108 isdisposed at a free end of the arm 106 and comprises detectable spheres110, 112 and 114 secured thereto. The detectable spheres 110, 112 and114 are similar in construction to the above mentioned detectablespheres 44, 46 and 48.

The calibration base C is adapted for receiving and releasably securingsurgical instruments having working shafts of a wide range ofcross-section shapes and diameters (e.g. 3 to 37 mm). In the preferredembodiment, instruments having circular cross-sections are used with thecalibration base C. As seen in FIG. 2, the surgical instrument S isabutted against the XZ plane 28 and the YZ plane 32 and is biased inthis position by the lever 38. By knowing the diameter of the workingshaft 100, it is possible to calculate the positioning of thelongitudinal axis thereof (i.e. at the center of the circularcross-section) which is possible with respect to the edge of thecalibration base C. Moreover, the surgical instrument S is disposed inthe calibration base C with the working tip 102 thereof touching the XYplane 14 of the base plate 10.

As the position and orientation of the detectable spheres 44, 46 and 48may be determined by sensors, and the position of these spheres on thecalibration base C is known as they are secured thereto, the positionand orientation of the working tip 102 of the surgical instrument S iscalculable as it is located at the intersection of the longitudinal axisof the working shaft 100 and the XY plane 14 of the calibration base C.

Although the preferred embodiment discloses planes 14, 28 and 32 allbeing in a perpendicular relation, it is pointed that the planes 14, 28and 32 may be in any relation with respect one to another so long as theposition of a given portion of the instruments is calculable. Forinstance, the planes 28 and 32 may define a V-shaped channel of obtuseor acute angles for receiving the working shaft 100 thereagainst, eventhough the preferred embodiment discloses a right angle therebetween.

Referring now to FIG. 6, a positioning system for calibrating thesurgical instrument S disposed in the calibration base C is generallyshown at 200, and comprises a position calculator 202. The positioncalculator 202 is a computer program, which may be, for instance,installed on the computer-aided surgery platform. The positioncalculator 202 receives space locations, including the position andorientation, of the detectable spheres 44, 46 and 48 of the calibrationbase C, and the detectable spheres 110, 112 and 114 mounted on thesurgical instrument S through sensors 204. The position calculator 202also receives instrument identification from an operator through userinterface 206. It is noted that the cross-sectional dimensions ofinstruments to be used with the position calculator 202 are storedthereby such as to be retrieved upon operator instrument identification.For instance, the operator may indicate that the instrument whoseworking tip is illustrated in one of FIGS. 3 to 5 is to be calibrated.In the event where the instrument information is not stored by theposition calculator 202, it is possible for the operator to enter newinformation amongst the instrument data 214 through the user interface206. The user interface 206 may comprise typical keyboard, mouse andmonitor.

It is noted that the space relation 208 of the detectable spheres 110,112 and 114 is stored by the position calculator 202, such that thelatter will recognize them through the sensors 204. Other informationstored by the position calculator 202 include the space relation 210 ofthe detectable spheres 44, 46 and 48, the space geometry 212 by thecalibration base C, including the space relation between these spheresand the calibration base C. Also, the cross-section shapes anddimensions 214 of the various tools to be used is stored by the positioncalculator 202. Once the position and orientation of the detectablespheres 44, 46 and 48 and the detectable spheres 110, 112 and 114 aredetected by the sensor 204, and the instrument is identified by theoperator through the user interface 206, the position and orientation ofthe working tip 102 of this instrument is calculated with respect to thedetectable spheres 110, 112 and 114 attached thereto, as explainedabove. This results in the calibration of the instrument, as prompted bythe position calculator 202 to the user interface 206 and as signaled tothe computer-aided surgery system 216.

The position calculator 202 also stores the prior calibration data 218,which consists in the calculated position and orientation of the tips ofall the instruments which have been calibrated previously. This allowsfor a validation of the calibration of the instruments. For instance,the instrument S depicted in FIG. 1 is calibrated and used for surgery.The position calculator 202 will automatically store the position andorientation of the working tip 102 of the instrument S with respect tothe position of the detectable spheres 110, 122 and 114 thereon.Thereafter, at the next calibration of the same instrument S, theposition calculator 202 will compare the new calculated position andorientation of the working tip 102 to the stored reference position andorientation. If the new calculated position and orientation are notwithin an allowable range, the operator will be prompted to verify thestate of the instrument and the positioning thereof in the calibrationbase C. If, after a second reading of the sensors 204 the position andorientation is the same as the previous one, the operator will beprompted to either accept the new space position and orientation, or toretry calibrating until the stored reference position and orientationare attained.

In the preferred embodiment, the calibration base C is constructed inaccordance with high standards of precision such that the XY plane 14,the XZ plane 28 and the YZ plane 32 are all planar and in perpendicularrelationship. Although other configurations are possible, the abovedescribed geometry of the calibration base C provides a simple solution.

The calibration base C is permanently calibrated as it does not changeshape. As mentioned above, the calibration C is made of a material whichcan sustain great impacts (i.e. stainless steel). Also, as seen in FIG.2, the first protrusion 22 and the second protrusion 24 are provided inorder to protect the detectable spheres 44, 46 and 48 in case of a fallof the calibration base C.

Although the use of retro-reflective spheres has been described above,it is pointed out that the detection of the position and orientation ofthe instrument S and the calibration base C may be achieved by otherdevices such as magnetic sensors, ultrasound sensors and infrared LEDs.Referring to FIG. 7, a housing 43 is shown mounted to the calibrationbase C, whereas a housing 113 is shown secured to the surgicalinstrument S. The housings 43 and 113 may contain either magneticsensors, ultrasound sensors or the like.

The use of the lever 38, for releasably securing the instrument Sensures the precise positioning of the latter with respect to the XZplane 28 and the YZ plane 32 and is adapted for receiving shafts ofvarious diameters (e.g. 3 to 37 mm) with its rounded end 40. It ispointed out that alternative mechanisms may be used instead of thespring-biased lever 38, so long as the working shaft is pressuredagainst the planes 28 and 32. Gravity forces the tip 102 of theinstrument S against the XY plane 14 in the preferred embodiment, thusrendering the above-described releasable connection virtuallyinstantaneous.

The arm 106 of the surgical instrument S is of a material which issubstantially less resistant to impacts than the blade 108. Therefore,in the event of a great impact on the surgical instrument S, the arm 106would get deformed before the blade 108, thereby protecting the geometrythereof which defines the space positioning of the detectable spheres110, 112 and 114 and is stored at 208 by the position calculator 102.Thus, if the arm 106 is damaged, the surgical instrument S may bequickly recalibrated according to the above described method in order toset the location of its tip 102 in space.

1. A calibration base to automatically calibrate any of a plurality ofinstruments having varying cross-sectional dimensions within apredetermined range for computer-aided surgery, each of the instrument,having a detectable portion, a working shaft and a tip at an end of theworking shaft, said calibration base comprising; first detectable meanssecured thereto for detecting a position and an orientation thereof inspace by sensor means connected to a position calculator; and saidcalibration base adapted to receive and to releasably secure the workingshaft of any of the instruments and providing a first abutting surfacefor the tip thereof in such a way that a position and orientation of thetip of any of the instruments secured therein is calculable when workingshaft cross-section dimensions thereof are known; whereby any of theinstruments is calibrated when the position and orientation of the tipof the working shaft thereof is calculated.
 2. The calibration base asdefined in claim 1, wherein the first abutting surface extends in adirection generally opposed to a longitudinal axis of the working shaftof any one of the instruments.
 3. The calibration base as defined inclaim 2, wherein the working shaft of any of the instruments is abuttedagainst a second and a third abutting surface.
 4. The calibration baseas defined in claim 3, wherein said second, and said third abuttingsurfaces define a V-shaped channel.
 5. The calibration base as definedin claim 4, wherein said first, second end third abutting surfaces areeach in a perpendicular relation with respect one to another.
 6. Thecalibration base as defined claim 1, wherein the working shaft of anyone of the instruments is releasably secured against abutting surfacesof said calibration bass by a biasing member.
 7. The calibration base asdefined in claim 6, wherein said biasing member comprises aspring-loaded lever.
 8. The calibration base as defined in claim 7,wherein said lever has a generally rounded end surface for engagingcontact with the working shaft.
 9. The calibration base as defined inclaim 1, wherein said first detectable means comprises three opticallydetectable spheres.
 10. The calibration base as defined in claim 9,wherein each said detectable sphere is retro-reflective.
 11. Thecalibration base as defined in claim 9, wherein said detectable spheresare detachable from said calibration base.
 12. The calibration base asdefined in claim 1, wherein said first detectable means are disposed ina concavity of said calibration base for impact protection thereof. 13.The calibration base as defined in claim 12, wherein said concavity iscomprised of at least a pair of protrusions.
 14. A method forcalibrating any of a plurality of instruments having varyingcross-sectional dimensions within a predetermined range with a positioncalculator connected to sensor means for computer-aided surgery, any oneof the instruments having first detectable means being secured theretoand being releasably secured for calibration in a calibration basehaving second detectable means, said method comprising the steps of: (i)detecting a position and orientation in space of said first and seconddetectable means by said sensor means; (ii) receiving instrument data;and (iii) calculating a position and orientation of a tip of any one ofthe instruments secured in said calibration base with respect to saidsecond detectable means as a function of said instrument data wherebythe instrument is calibrated with respect to said first detectablemeans.
 15. The method as defined in claim 14, wherein the step (ii)includes receiving said instrument data from an operator through a userinterface.
 16. The method as defined in claim 14, wherein the step (iii)includes comparing the calculated position and orientation with a storedreference position and orientation of the tip of a same instrument ascalculated in a previous calibration of the same instrument.
 17. Themethod as defined in claim 16, wherein the step (iii) includes promptingan operator to verify the instrument if the calculated position andorientation is outside tolerances of the position and orientation of theprevious calibration of the same instrument and waiting for an operatorsignal to proceed with a subsequent calibration calculation.
 18. Themethod as defined in claim 17, wherein the step (iii) is repeated untilthe position and orientation of the previous calibration of the sameinstrument within said tolerances is attained.
 19. The method accordingto claim 18, wherein the step (iii) includes asking the operator aboutsetting a same position and orientation as calculated by at least twosubsequent calibration calculation as a new accepted calibrationcalculation.
 20. The method as defined in claim 15, wherein saidinstrument data includes one of identification data relating toinstrument cross sectional dimension data stored by said positioncalculator and of instrument cross-sectional dimension data to be storedby said position calculator for subsequent calibrations.
 21. A positioncalculator computer program product comprising code means recorded in acomputer readable memory for executing a method for calibrating any of aplurality of instruments having varying cross-sectional dimensionswithin a predetermined range with a position calculator connected tosensor means for computer-aided surgery, any one of the instrumentshaving first detectable means being secured thereto and being releasablysecured for calibration in a calibration base having second detectablemeans, said method comprising the steps of: (i) detecting a position andorientation in space of said first and second detectable means by saidsensor means; (ii) receiving instrument data; and (iii) calculating aposition and orientation of a tip of any one of the instruments securedin said calibration base with respect to said second detectable means asa function of said instrument data whereby the instrument is calibratedwith respect to said first detectable means.
 22. A System for automaticcalibration of instruments for computer-aided surgery, comprising: acalibration base to automatically calibrate any of a plurality ofinstruments having varying cross-sectional dimensions within apredetermined range for computer-aided surgery, each of the instrumentshaving a detectable portion, a working shaft and a tip at an end of theworking shaft, said calibration base comprising first detectable meanssecured thereto for detecting a position and an orientation thereof inspace by sensor means connected to a position calculator, and saidcalibration base adapted to receive and to releasably secure the workingshaft of any of the instruments and providing a first abutting surfacefor the tip thereof in such a way that a position and orientation of thetip of any of the instruments secured therein is calculable when workingshaft cross-section dimensions thereof are known, whereby any of theinstruments is calibrated when the position and orientation of the tipof the working shaft thereof is calculated; said detectable portion onthe instruments comprising second detectable means for space positioningof the instruments, said second detectable means being adapted to besecured to any of the instruments; said sensor means for detecting aposition and orientation in space of said first and second detectablemeans; and a position calculator connected to said sensor means forcalculating a position and orientation of the tip of the working shaftof any of the instruments secured in said calibration base with respectto the first detectable means according to a method comprising the stepsof (i) detecting a position and orientation in space of said first andsecond detectable means by said sensor means, (ii) receiving instrumentdata, and (iii) calculating a position and orientation of a tip of anyone of the instruments secured in said calibration base with respect tosaid first detectable means as a function of said instrument data;whereby any of the instruments is calibrated with respect to said seconddetectable means when the position and orientation of the tip of theworking shaft thereof is calculated.
 23. The system as claimed in claim22, wherein said second detectable means comprises three other opticallydetectable spheres.
 24. The system as claimed in claim 23, wherein eachsaid other detectable sphere is retro-reflective.
 25. A method forcalibrating instruments with a position calculator connected to sensormean for computer-aided surgery, the instruments having detectable meansbeing secured thereto, said method comprising the steps of: (i)detecting a position and orientation in space of said detectable meansby the sensor means; (ii) calculating a position and orientation of apredetermined portion of any one of the instruments with respect to saiddetectable means; and (iii) comparing the calculated position andorientation with a stored reference position and orientation of thepredetermined portion of a same instrument as calculated in a previouscalibration of the same instrument, and prompting an operator to verifythe instrument if the calculated position and orientation is outsidetolerances of the position and orientation of the previous calibrationof the same instrument and waiting for an operator signal beforerepeating the steps (i), (ii) and (iii), whereby the instrumentcalibration is validated if the calculated position and orientation iswithin tolerances of the position and, orientation of the previouscalibration of the same instrument.
 26. The method as defined in claim25, wherein the step (iii) is repeated until the position andorientation of the previous calibration of the same instrument withinsaid tolerances is attained.
 27. The method as defined in claim 26,wherein the step (iii) includes asking the operator about setting a sameposition and orientation as calculated by at least two subsequentcalibration calculation as a new accepted calibration calculation. 28.The method as defined in claim 25, wherein the step (iii) includesaccepting instrument identification data from a user, storing theposition and orientation from the previous calibration in associationwith the identification data and requesting the user to identify theinstrument prior to the steps (i), (ii) and (iii).
 29. A positioncalculator computer program product comprising code means recorded in acomputer readable memory for executing a method for calibratinginstruments with a position calculator connected to sensor means forcomputer-aided surgery, the instruments having detectable means beingsecured thereto, said method comprising the steps of: (i) detecting aposition and orientation in space of said detectable means by the sensormeans, (ii) calculating a position and orientation of a predeterminedportion of any of one of the instruments with respect to said detectablemeans; and (iii) comparing the calculated position and orientation witha stored reference position and orientation of the predetermined portionof a same instrument as calculated in a previous calibration of the nameinstrument, and prompting an operator to verify the instrument if thecalculated position and orientation is outside tolerances of theposition and orientation of the previous calibration of the nameinstrument and waiting for an operator signal before repeating the steps(i), (ii) and (iii); whereby the instrument calibration is validated ifthe calculated position and orientation is within tolerances of theposition and orientation of the previous calibration of the sameinstrument.